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Active Coils
(na)
Those coils which are free to deflect under
load.
Angular
relationship of
ends
The relative position of the plane of the
hooks or loops of
extension springs to each
other.
Baking
Heating of electroplated springs to relieve
hydrogen
embrittlement.
Buckling
Bowing or lateral deflection of compression
springs when
compressed, related to the slenderness ratio
(L/D).
Closed
ends
Ends of compression springs where pitch of
the end coils is
reduced so that the end coils
touch.
Closed and
Ground
Ends
As with closed ends, except that the end is
ground to
provide a flat plane.
Closed
length
See Solid height.
Close-wound
Coiled with adjacent coils
touching.
Coils per
inch
See Pitch.
Deflection
(F)
Motion of spring ends or arms
under the
application or removal of an external load (P).
Elastic
limit
Motion of spring ends or arms
under the
application or removal of an external load (P).
Endurance
limit
Maximum stress at which any
given material
will operate indefinitely without failure
for a given minimum stress.
Free
angle
Angle between the arms of a torsion spring
when the spring
is not loaded.
Free length
(L)
The overall length of a spring in the
unloaded
position.
Frequency
(natural)
The lowest inherent rate of free vibration
of a spring
itself (usually in cycles per second) with
ends restrained.
Gradient
See Rate (R).
Heat
setting
Fixturing a spring at elevated temperature
to minimize loss
of load at operating
temperature.
Helix
The spiral form (open or closed) of
compression, extension,
and torsion
springs.
Hooke's
Law
Load is proportional to
displacement.
Hooks
Open loops or ends of extension
springs.
Hot
Pressing
See Heat Setting.
Hydrogen
Embrittlement
Hydrogen absorbed in electroplating or
pickling of carbon
steels, tending to make the spring
material brittle and susceptible to cracking
and failure,
particularly under sustained
loads.
Hysteresis
The mechanical energy loss that always
occurs under cyclic
loading and unloading of a spring,
proportional to the area between the loading
and unloading
load-deflection curves within the elastic range of a
spring.
Initial
Tension
(Pi)
The force that tends to keep the coils of
an extension
spring closed and which must be overcome
before the coils start to
open.
Load
(P)
The force applied to a spring that causes a
deflection
(F).
Loops
Coil-like wire shapes at the ends of
extension springs that
provide for attachment and force
application.<
Mean Coil
Diameter
(D)
Outside spring diameter (O.D.) minus one
wire diameter
(d).
Modulus in
Shear or Torsion
(G)
Coefficient of stiffness for extension and
compression
springs.
Modulus in
Tension or Bending
(E)
Coefficient of stiffness used for torsion
and flat springs
(Young's Modulus).
Moment
(M)
See Torque.
Open Ends, not
Ground
End of a compression spring with a constant
pitch for each
coil.
Open Ends Ground
"Open ends, not ground" followed by an end
grinding
operation.
Passivating
Acid treatment of stainless steel to remove
contaminants and
improve corrosion
resistance.
Permanent
set
A material that is deflected so far that
its elastic
properties have been exceeded and it does not
return to its original condition
upon release of load is
said to have taken a "permanent set."
Pitch
(p)
The distance from center to center of the
wire in adjacent
active coils (recommended practice is to
specify number of active coils rather
than
pitch).
Poisson's
Ratio
The ratio of the strain in the transverse
direction to the
strain in the longitudinal
direction.
Preset
See Remove set.
Rate
(R)
Change in load per unit deflection,
generally given in
pounds per inch.
(N/mm)
Remove
set
The process of closing to solid height a
compression spring
which has been coiled longer than the
desired finished length, so as to increase
the apparent
elastic limit.
Residual
stress
Stresses induced by set removal, shot
peening, cold working,
forming or other means. These
stresses may or may not be beneficial, depending
on the
application.
Set
Permanent distortion which occurs when a
spring is stressed
beyond the elastic limit of the
material.
Shot
peening
A cold-working process in which the
material surface is
peened to induce compressive stresses
and thereby improve fatigue
life.
Slenderness
ratio
Ratio of spring length (L) to mean coil
diameter
(D).
Solid height
(H)
Length of a compression spring when under
sufficient load to
bring all coils into contact with
adjacent coils.
Spring
index
Ratio of mean coil diameter (D) to wire
diameter
(d).
Squared and
ground
ends
See Closed and ground ends.
Squared
ends
See Closed ends.
Squareness of
ends
Angular deviation between the axis of a
compression spring
and a line normal to the plane of the
ends.
Squareness
under load
As in Squareness of ends, except with the
spring under
load.
Stress
range
The difference in operating stresses at
minimum and maximum
loads.
Stress
relieve
To subject springs to low-temperature heat
treatment so as
to relieve residual
stresses.
Torque
(M)
A twisting action in torsion springs which
tends to produce
rotation, equal to the load multiplied by
the distance (or moment arm) from the
load to the axis of
the spring body. Usually expressed in oz./in., lb./in.,
lb./ft., or in. N/mm.
Total number
of coils
(Nt)
Number of active coils (Na) plus the coils
forming the
ends.
Wahl
Factor
A factor to correct stress in helical
springs effects of
curvature and direct shear.